1. Field of the Invention
The present invention relates to an apparatus and method for direct or indirect application of a liquid or pasty medium onto a traveling material web, notably of paper or cardboard.
2. Description of the Related Art
Apparatuses and methods as described above are known in multifarious configurations. Prior apparatuses include applicators resting on a support beam and configured either for direct or indirect application of a liquid or pasty coating medium onto a traveling material web or for finish-dosing of a coating medium applied previously onto the material web. The application of the coating medium usually takes place via a pressure chamber with a doctor element, an open-jet nozzle or a comparable other applicator. In the so-called direct application, the coating medium is applied directly onto the traveling material web, supported, e.g., by a backing roll opposing the support beam, while in the indirect application the coating medium is transferred first, e.g., onto an applicator roll opposing the support beam and then, from its surface, onto the material web. In the second case, i.e., with an applicator for finish-dosing, a doctor blade or a comparable other known doctor element is employed to finish-dose the coating substance applied already on the material web, to the desired amount of application. Known from DE 4 130 118 C2 is a categorical apparatus for direct or indirect application of a liquid or pasty medium onto a traveling material web, notably of paper or cardboard, with a support beam that extends lengthwise substantially across the entire width of the material web. The apparatus is supported at two bearing points and includes a finish-dosing apparatus in the form of a doctor blade, a doctor bar or a scraper bar. With this apparatus, the two bearing points rest in two long pivot arms disposed on the outer ends of the support beam, i.e., outside the width of the traveling material web, and serve to pivot the support beam about an axis parallel to the support beam axis to a working position, intermediate position and maintenance position. This type of apparatus, however, not only has the drawback of problematic support beam flexures and comparably low natural frequencies that lead to undesirable resonances, for example, with oscillation frequencies of the pedestal of the apparatus or of the floor of the hall in which the apparatus is installed, but such an apparatus requires additionally a very large, massive and thus heavy and cost-intensive pivoting device. An adaptation to changing operating conditions, such as changing backing roll diameters, wear of the finish-dosing apparatus, change of the coating angle adjustment between finish-dosing apparatus and backing roll, or a change of the finish-dosing apparatus pressure, is possible with this apparatus only at considerable expense and sometimes is not possible at all. Quick pivotal motions of the support beam can be carried out only with the use of powerful and thus expensive actuators, due to the large masses to be moved and the long lever arms.
With conventional apparatuses, furthermore, it has proved to be problematic that, when using doctor blades as finish-dosing apparatus, for one, an adjustment of the blade angle, that is, the angle between the doctor blade and a tangent laid to the opposing applicator roll, by pivoting the support beam leads to an undesirable change of the blade pressure or even to a liftoff of the doctor blade and, for another, a change of the blade pressure leads to an undesirable change of the blade angle and thus to irregularities of the coating profile, which reduces the quality of the finished product.